This invention relates generally to producing impurity concentration profiles in solids and particularly to methods of producing semiconductor devices and optical waveguides.
Establishing an impurity concentration profile in a solid, and particularly a buried layer of impurity, has usefulness in many fields. For example, a semiconductor material with a buried layer of a substance with different electrical properties would be useful in semiconductor circuits. A buried layer with a different index of refraction than the host material could be utilized in producing optical waveguide devices.
In preparation of semiconductor devices, a wide variety of techniques have been used to produce impurity profiles. They fall into three major catagories:
A. Variation of crystal growing conditions PA1 B. Diffusion methods PA1 C. Ion implantation
Of these, only ion implantation is capable of producing thin layer profiles near the surface of samples. Ion implantation has also been successful in producing layer structures required for optical waveguides. Nevertheless it has the drawback that the bombardment also causes damage to the sample, in the form of various lattice defects. Another difficulty has been that the incident ions do not all incorporate into the material in the same manner, some being substitutional and other occupying interstitial positions and defect sites. Besides these operational problems there is also the practical consideration that ion implantation requires and expensive accelerator and technical expertise not available in most facilities.
Other methods of producing optical waveguides include sputtering, evaporation, liquid phase epitaxy, plasma polymerization and ion exchange. The last of these is capable of producing buried layers, as is ion implantation. However the layers produced by ion exchange are typically about an order of magnitude thicker than those produced by implantation. The ion exchange method has the drawbacks that it typically requires several hours of processing, involves the use of molten salt baths and is only feasible in certain chemical systems.
It is therefore an object of this invention to provide a method for establishing one or more layer profiles in a solid which is fast, simple, inexpensive, and versatile.
Also, an object of this invention is to provide a method of establishing a greater variety of profiles in solids which may be tailored to specifc applications.
Another object of this invention is to provide a method of establishing layer profiles in solids which utilizes a fast laser pulse.
Another object of this invention is to provide a method of producing small local regions of impurity penetration in a large extended solid sample.
YET ANOTHER OBJECT OF THIS INVENTION IS TO PROVIDE A METHOD OF ESTABLISHING IMPURITY LAYER PROFILES IN SOLIDS WHICH CAN BE CONTROLLED SO AS TO PRODUCE MINIMUM DAMAGE TO CRYSTALLINE MATERIALS.
And yet another object of this invention is to provide a method of establishing impurity layer profiles at an accurate depth in a solid.
Also, an object of this invention is to provide a method of establishing impurity layer profiles in solids which can be carried out at atmospheric pressure.
And another object of this invention is to provide a method of establishing impurity layer profiles which have variable concentrations.
And a further object of this invention is to provide a method of producing concentration profiles using a process having a duration of less than 1 .mu.s.
These and other objects are achieved by attaching a solid with an impurity to a heat sink and flash melting the solid by short low energy laser pulses whereby a freezing interface passes from the heat sink into the interior of the solid which causes the impurity to move into the interior of the solid with a particular concentration profile.